Mechanism: Nociceptors Flashcards
What is the main mechanism of pain?
The main mechanism of pain is a result of activation of nociceptors.
What type of pain is this involved in?
Inflammatory pain
What are nociceptors and where are they located?
Nociceptors are the specialised sensory receptors responsible for the detection of noxious stimuli (mechanical, thermal or chemical), transforming the stimuli into electrical signals which are then conducted the central nervous system. They are the free nerve endings of primary afferent Adelta and C fibres.
They are distributed throughout the skin enabling them to respond to mechanical, thermal or chemical stimuli.
What do inflammatory mediators do?
Inflammatory mediators (bradykinin, serotonin, prostaglandins, cytokines) are release from damaged tissue and directly stimulate nociceptors.
What are Adelta fibres and what is their structure?
Primary sensory nerve fibre towards CNS. They are lightly myelinated with a small diameter.
What do Adelta fibres respond to?
Mechanical and thermal stimuli
What type of pain do Adelta fibres stimulate?
Rapid and sharp pain, responsible for initial reflex to acute pain.
What are C fibres and what is their structure?
Primary sensory neurons towards CNS. Unmyelinated so slowest conduction.
What do C fibres respond to?
Chemical stimuli
What type of pain do C fibres stimulate?
Slow, burning pain. Cause vasodilation leading to characteristic swelling.
What and where do Ad and C synapse to?
Ad and C both synapse with secondary afferent nociceptive-specific neurons in the dorsal horn of the spinal cord.
How does this connection transmit pain?
Primary afferent terminal release a number of excitatory NTs such as gluatamate and substance P. These peptides active their receptors producing slow depolarising response of dorsal horn neurones whilst simultaneously activating fast AMPA receptors responsible for acute touch and pain and delayed NMDA receptors rapidly enhancing pain.
These complex interactions in the dorsal horn determine activity of secondary afferent neurons.
How does the signal reach the brain?
There are 2 main pathways that carry nociceptive signals to higher centres in the brain.
What are the 2 pathways?
- Spinothalamic tract - transmits signal important for pain localisation.
- Spinoreticular tract - involved in emotional aspects of pain
How is pain processed in the brain?
‘Pain-matrix’ = pain results from multitude of interactions in brain
The ascending messages to the brain run to the thalamus and cortex where the location and intensity of pain are perceived.
At the same time other pathways run to the limbic system where the psychological aspects (fear, anxiety, insomnia) are established.
